1. Field of the Invention
The present invention relates to an improved inkjet printing head applicable to a printer, a facsimile machine, a plotter and so on.
2. Description of the Related Art
There are known inkjet printing methods in which printing is performed by jetting ink from nozzles onto a recording medium such as paper without bringing a printing head into contact with the recording medium. One typical example of such a method is the drop-on-demand type inkjet printing method, in which ink drops are produced only when needed. With a printing head operating according to this method, a voltage is applied to a piezoelectric element, which varies the volume of a pressure chamber housing ink. Then, ink is caused to fly at the paper via a nozzle in communication with the pressure chamber. Such a printing head mainly comprises a head plate including a plurality of pressure chambers, a diaphragm, and a plurality of piezoelectric elements.
The pressure chambers and piezoelectric elements are arranged in various ways on the head plate in accordance with printing head specifications. For instance, a printing head of a line printer includes pressure chambers and piezoelectric elements which are arranged in a line so that nozzles are aligned along a printing line. With a serial printer, a printing head includes pressure chambers and piezoelectric elements which are radially arranged in a space extending through 180xc2x0 or more.
In the inkjet printing head, a diaphragm in the shape of a thin film is attached onto a head plate carrying a plurality of pressure chambers thereon. A plurality of piezoelectric elements are arranged on the diaphragm such that they respectively correspond to the pressure chambers. The piezoelectric elements are respectively actuated by a voltage applied thereto, thereby causing the corresponding parts of the diaphragm to shudder. The shuddering of the diaphragm is transmitted to pressure chambers, thereby flexing them. Then, ink is jetted from nozzles in communication with the pressure chambers. Conversely, when the voltage application is stopped, the diaphragm restores, sucking ink from an ink delivery area, and preparing for a subsequent ink jetting operation. Specifically, the respective piezoelectric elements are actuated in response to printing data supplied from an external source, and vary the volume of necessary pressure chambers. According to the varied volume, the nozzles jet a desired amount of ink onto a recording medium so as to print an image thereon.
The foregoing inkjet printing head comprises a head assembly, a cable, an ink reservoir, and an ink pipe. The head assembly includes a head plate, a diaphragm, and a plurality of piezoelectric elements. The head plate carries a plurality of pressure chambers and nozzles disposed thereon. The cable includes a group of electrodes respectively applying a voltage to their associated piezoelectric elements, and 49 control wires (i.e. at least 48 signal wires and one grounding wire when an inkjet printing head has 48 piezoelectric elements). Ink is supplied to the head assembly via the ink pipe from the ink reservoir. Particularly, it is extremely difficult to precisely contact piezoelectric elements with their corresponding electrodes and connect the ink pipe with them so as to prevent ink leakage when assembling a printing head. Therefore, there is a problem that the printing head takes time to be assembled, and that the cable including the control wires is difficult to handle. This means that the printing head cannot be assembled efficiently.
The present invention is aimed at overcoming the foregoing problems of the related art, and providing an inkjet printing head which can be assembled efficiently.
According to a first aspect of the invention, there is provided an inkjet printing head comprising: a head assembly which includes a plurality of pressure chambers, each pressure chamber having a nozzle at one end and an ink inlet at the other end thereof, a plate defining an ink conduit in communication with the ink inlets, a diaphragm disposed over the pressure chambers, and a plurality of piezoelectric elements attached to one surface of the diaphragm in such a manner as to individually correspond to the pressure chambers, each piezoelectric element making the diaphragm shudder and varying a capacity of each pressure chamber so as to introduce ink into the pressure chamber and to jet ink via the nozzle; a main frame having a hollow portion at a center thereof and supporting the head assembly on one surface thereof; a flexible cable including a group of electrodes for applying a drive voltage to the piezoelectric elements; a flexible member attached to the other surface of the main frame, the flexible member keeping the piezoelectric elements and the flexible cable in mutual contact via the hollow portion of the main frame, and preventing the flexible cable from resonating due to shudders of the piezoelectric elements; and a sub-frame fixing the flexible cable and the flexible member to the main frame with pressure.
In this arrangement, the flexible cable and the flexible member are sandwiched between the main frame and sub-frame, so that it is possible to uniformly and reliably press the electrodes toward their associated piezoelectric elements via the flexible member.
Therefore, it is possible to prevent the flexible cable from resonating when the piezoelectric elements are actuated.
The main frame includes a recess for receiving the head assembly. The hollow portion of the main frame is shaped similarly to the flexible cable so to house the flexible cable therein. Thus, the main frame, head assembly and flexible cable are precisely and easily positioned with respect to one another.
The nozzles are inclined with respect to a printing line by a predetermined angle on the head assembly, both the hollow portion of the main frame and the flexible cable are oval in the shape, and the flexible cable is housed in the hollow portion. This enables not only a printing density to be improved without narrowing a pitch between the nozzles but also assures precise, reliable and easy positioning of the main frame, head assembly and flexible cable.
The sub-frame has a rimmed window capable of fitting into the hollow portion of the main frame, and the rimmed window supports the flexible member. Thus, the flexible cable and the flexible member are positioned easily and precisely with respect to each other. Further, it is possible to contact the flexible cable to the piezoelectric elements with a uniform pressure. Still further, the inkjet printing head can be automatically assembled by using a part feeder since no strict positioning of the components is necessary.
In accordance with a second aspect of the invention, there is provided an inkjet printing head comprising: a head assembly including a plurality of pressure chambers, each pressure chamber having a nozzle at one end and an ink inlet at the other end thereof, a plate defining an ink conduit in communication with the ink inlets, a diaphragm disposed over the pressure chambers, and a plurality of piezoelectric elements attached to one surface of the diaphragm in such a manner as to individually correspond to the pressure chambers, each piezoelectric element making the diaphragm shudder and varying a capacity of each pressure chamber so as to introduce ink into the pressure chambers and to jet ink via the nozzle; a main frame having a hollow portion at a center thereof and supporting the head assembly on one surface thereof; a flexible cable including groups of electrodes for applying a drive voltage to the piezoelectric elements; a flexible member attached to the other surface of the main frame, the flexible member keeping the piezoelectric elements and the flexible cable in mutual contact via the hollow portion of the main frame, and preventing the flexible cable from resonating due to shudders of the piezoelectric elements; and a sub-frame fixing the flexible cable and the flexible member to the main frame with pressure. The diaphragm includes an ink port for supplying ink to the ink conduit, and an ink pipe in communication with an ink reservoir is disposed close to the ink port.
In this arrangement, the ink pipe in communication with the ink reservoir is directly connected to the ink port.
Since no ink is in direct contact with the main frame, it is possible to protect the main frame against erosion caused by ink. In other words, since the nozzles are not blocked by metal or resin components in the main frame, the original quality of ink can be reliably maintained without color change.
Further, the ink pipe can be directly and intimately connected to the ink port, so that it is possible to supply ink without any leakage.
According to a third aspect of the invention, there is provided an inkjet printing head comprising: a head assembly, the head assembly including: a plurality of pressure chambers, each pressure chamber having a nozzle at one end and an ink inlet at the other end thereof; a plate defining an ink conduit in communication with the ink inlets; a diaphragm disposed over the pressure chambers; and a plurality of piezoelectric elements attached to one surface of the diaphragm in such a manner as to individually correspond to the pressure chambers, each piezoelectric element making the diaphragm shudder and varying a capacity of each pressure chamber so as to introduce ink into the pressure chamber and jet ink via the nozzle; a main frame having a hollow portion at a center thereof and supporting the head assembly on one surface thereof; a flexible cable including a group of electrodes for applying a drive voltage to the piezoelectric elements; a flexible member attached to the other surface of the main frame, the flexible member keeping the piezoelectric elements and the flexible cable in mutual contact via the hollow portion of the main frame, and preventing the flexible cable from resonating due to shudders of the piezoelectric elements; and a sub-frame fixing the flexible cable and the flexible member to the main frame with pressure. The diaphragm is smaller than the ink conduit plate so as to have a beginning of the ink conduit exposed from the diaphragm and form an ink port, and the ink pipe in communication with the ink port is positioned close to the beginning of the ink conduit.
The ink pipe in communication with the ink reservoir is directly connected to the ink port, so that ink does not come into contact with the main frame.
Further, the ink port can be easily formed without specifically modifying the diaphragm or ink conduit plate. This will lead to reduction of the manufacturing cost of the inkjet printing head.
The beginning of the ink conduit is joined to the ink pipe via flexible packing so as to seal a joined portion.
A curing resin is applied to a step portion between the ink conduit plate and the diaphragm so as to form a slope thereon, which reliably and easily connects the ink pipe.
Further, the curing resin is applied so as to be banked against a peripheral area of the beginning of the ink port. This enables the ink pipe to be sealed reliably.
When the curing resin is applied so as to be banked around the beginning of the ink conduit, the joined portion of the ink pipe can be reliably sealed.
Further, a filter is closely attached to the ink port using the curing resin so as to filter impurities in the ink. The filter is integral with the joined area of the ink pipe, which can reduce the number of components used, and assures reliable connection of the ink pipe without ink leakage.
In a fourth aspect of the invention, there is provided an inkjet printing head comprising: a head assembly, the head assembly including: a plurality of pressure chambers, each pressure chamber having a nozzle at one end and an ink inlet at the other end thereof; a plate defining an ink conduit in communication with the ink inlets; a diaphragm disposed over the pressure chambers; and a plurality of piezoelectric elements attached to one surface of the diaphragm in such a manner as to individually correspond to the pressure chambers, each piezoelectric element making the diaphragm shudder and varying a capacity of each pressure chamber so as to introduce ink into the pressure chambers and to Jet ink via the nozzle; a main frame having a hollow portion at a center thereof and supporting the head assembly on one surface thereof; a flexible cable including a group of electrodes for applying a drive voltage to the piezoelectric elements; a flexible member attached to the other surface of the main frame, the flexible member keeping the piezoelectric elements and the flexible cable in mutual contact via the hollow portion of the main frame, and preventing the flexible cable from resonating due to shudders of the piezoelectric elements; a sub-frame fixing the flexible cable and the flexible member to the main frame with pressure; and a driver IC attached on the flexible cable so as to perform central control of the piezoelectric elements.
In this arrangement, only control wires for controlling the driver IC extend out from the inkjet printing head.
Since a width of a bundle of the control wires can be reduced without thinning respective control wires, the control wires are durable. The reduced width of the control wire bundle can decrease a space for attaching the inkjet printing head to a printer body. This is advantageous for making the printer compact.
Such an inkjet printing head can be easily handled and efficiently attached to the printer body.
The flexible cable carrying the driver IC is sandwiched between the main frame and sub-frame, which allows the inkjet printing head to be efficiently assembled.
An external connection terminal is attached to one end of the flexible cable so as to receive a signal actuating the driver IC. This enables the printer body and the inkjet printing head to be fabricated separately, and to be joined at a later stage. The inkjet printing head becomes easy to handle and to connect to the printer body. Further, a faulty inkjet printing head can be easily replaced with a new one.
Since the driver IC is positioned on a recess of the rear surface of the main frame, the main frame and the sub-frame can be brought into close contact with each other. Thus, the electrodes on the flexible cable can be uniformly pressed to the piezoelectric elements on the main frame.
Alternatively, when the driver IC is positioned on a recess on a surface of the sub-frame where it is pressed to the main frame, the main frame and the sub-frame can be brought into close contact so as to sandwich the flexible cable carrying the driver IC. Therefore, the electrodes on the flexible can be pressed to the piezoelectric elements on the main frame with uniform force.